The present invention relates to packaging of microelectronic devices, especially the packaging of semiconductor devices. The present invention also relates to stacked microelectronic packages including stacked microelectronic packages fabricated at the wafer level and to methods of making such packages.
Microelectronic elements generally comprise a thin slab of a semiconductor material, such as silicon or gallium arsenide, commonly called a die or a semiconductor chip. Semiconductor chips are commonly provided as individual, prepackaged units. The active circuitry is fabricated in a first face of the semiconductor chip (e.g., a front surface). To facilitate electrical connection to the active circuitry, the chip is provided with bond pads on the same face. The bond pads are typically placed in a regular array either around the edges of the die or, for many memory devices, in the die center. The bond pads are generally made of a conductive metal, such as copper, or aluminum, around 0.5 μm thick. The bond pads could include a single layer or multiple layers of metal. The size of the bond pads will vary with the device type but will typically measure tens to hundreds of microns on a side.
In some unit designs, the semiconductor chip is mounted to a substrate or chip carrier, which is in turn mounted on a circuit panel, such as a printed circuit board. Semiconductor chips are typically packaged with substrates to form microelectronic packages having terminals that are electrically connected to the chip contacts. The package may then be connected to test equipment to determine whether the packaged device conforms to a desired performance standard. Once tested, the package may be connected to a larger circuit, e.g., a circuit in an electronic product such as a computer or a cell phone.
In order to save space, certain conventional designs have stacked multiple microelectronic chips within a package. This allows the package to occupy a surface area on a substrate that is less than the total surface area of the chips in the stack. However, conventional stacked packages have disadvantages of complexity, cost, thickness and testability.
Size is a significant consideration in any physical arrangement of chips. The demand for more compact physical arrangements of chips has become even more intense with the rapid progress of portable electronic devices. Merely by way of example, devices commonly referred to as “smart phones” integrate the functions of a cellular telephone with powerful data processors, memory and ancillary devices such as global positioning system receivers, electronic cameras, and local area network connections along with high-resolution displays and associated image processing chips. Such devices can provide capabilities such as full internet connectivity, entertainment including full-resolution video, navigation, electronic banking and more, all in a pocket-size device. Complex portable devices require packing numerous chips into a small space. Moreover, some of the chips have many input and output connections, commonly referred to as “I/O's.” These I/O's must be interconnected with the I/O's of other chips. The interconnections should be short and should have low impedance to minimize signal propagation delays. The components which form the interconnections should not greatly increase the size of the assembly. Similar needs arise in other applications as, for example, in data servers such as those used in internet search engines. For example, structures which provide numerous short, low-impedance interconnects between complex chips can increase the bandwidth of the search engine and reduce its power consumption.
In spite of the above advances, there remains a need for improved semiconductor device and carrier packages and stacked packages that are reliable, thin, testable, and that are economical to manufacture. These attributes of the present invention are achieved by the construction of the microelectronic packages as described hereinafter.